Polyester film roll

ABSTRACT

The polyester film roll, which is free from wrinkles and slacks generated with the passage of time and is having a good roll appearance, is provided without changing the characteristics of the film.  
     The polyester film roll is a polyester film roll in which a polyester film is rolled on a core, characterized in that the difference R (m) between the maximum value and the minimum value is not more than 2W×10 −3  and not more than L×10 −7 , when the diameters of said roll are measured in the width direction of the roll, (therein, W is the width (m) of the film roll, and L is the rolled length (m) of the film roll), or  
     a polyester film roll in which a polyester film is rolled on a core, characterized in that, among the lengths of lines which are obtained by measuring the diameters of said roll in the width direction of the roll, drawing a straight line between both the ends of the curved line of the obtained roll diameters, and then vertically drawing the lines from said curved line to said straight line, the maximum length (maximum convex portion) on the convex portion side from said straight line is not more than 500 μm, and the maximum length (maximum concave portion) on the concave portion side from said straight line is not more than 300 μm.

TECHNICAL FIELD

[0001] The present invention relates to a polyester film roll, in moredetail, to a polyester film roll which is free from the generation ofwrinkles on the film and has a good roll appearance.

BACKGROUND ART

[0002] The polyester films have excellent in strengths, dimensionalstability, and so on, and have widely been used for magnetic recordingmedia, capacitors, packages and printing materials. Video tapes, audiotapes, computer tapes, and so on, are widely known as the magneticrecording media using the polyester films as supports (base films).

[0003] High density recordings on the magnetic recording media areprogressed in recent years, accompanied by the formation of thin andflat base films. However, it is difficult to roll a thin flat film in aroll-like shape in a good rolled appearance. Even when the thickness ofa film is slightly uneven, the unevenness of the film is accumulated,when rolled in the roll-like shape. Consequently, the thin portion offilm is deformed into a wrinkle-like shape, and the thick portion of thefilm is extended and forms slacks, when the film is unrolled, wherebytroubles are caused when the film is subjected to a processing such as acoating processing or a vacuum-deposition processing.

[0004] In order to solve the problems, various techniques such as theimprovement in the surface characteristics of a film [JP-A 59-95116(hereafter, JP-A means Japanese unexamined patent publication), JP-A59-171623, JP-A 2-194924, JP-A 3-207727, and so on], the reduction ofthickness unevenness (JP-A 48-43772, JP-A 52-47070, JP-A 54-56674, JP-A1-95025, JP-A 1-295822, and so on), or the dispersion of the thicknessunevenness into the width direction by oscillation (JP-A 36-22875, JP-A39-14534, and so on] have been proposed.

DISCLOSURE OF THE INVENTION

[0005] However, the conventional techniques had problems such as aproblem in which the characteristics of the film have to be changed, aproblem in which wrinkles or slacks are generated with the passage oftime, even when the film does not have a problem in a rolled state, anda problem in which a technique can not be applied to a practicalproduction, because the development of the technique is extremelydifficult. Especially, such the problems have been actualized, when thefilms are thinned and flattened.

[0006] The purposes of the present invention is to improve the problems,and to provide a polyester film roll which does not change thecharacteristics of the film, is free from the generation of wrinkles andslacks which are generated with the passage of time, and has a good rollappearance.

[0007] According to the present invention, the above-described purposesand advantages of the present invention are achieved, firstly, by apolyester film roll (hereinafter often referred to as the firstpolyester film roll) in which a polyester film is rolled on a core,characterized in that the difference R (m) between the maximum value andthe minimum value is not more than 2W×10⁻³ and not more than L×10⁻⁷,when the diameters of said roll are measured in the width direction ofthe roll. Therein, W is the width (m) of the film roll, and L is therolled length (m) of the film roll.

[0008] According to the present invention, the above-described purposesand advantages of the present invention are achieved, secondly, by apolyester film roll (hereinafter often referred to as the secondpolyester film roll) in which a polyester film is rolled on a core,characterized in that, among the lengths of lines which are obtained bymeasuring the diameters of said roll in the width direction of the roll,drawing a straight line between both the ends of the curved line of theobtained roll diameters, and then vertically drawing the lines from saidcurved line to said straight line, the maximum length (maximum convexportion) on the convex portion side from said straight line is not morethan 500 μm, and the maximum length (maximum concave portion) on theconcave portion side from said straight line is not more than 300 μm.

PREFERABLE EMBODIMENT OF THE INVENTION

[0009] Hereinafter, the first polyester film roll of the presentinvention will be explained.

[0010] The polyester film in the present invention may be an unorientedfilm or a monoaxially oriented film, but is preferably a biaxiallyoriented film especially oriented in the longitudinal direction (machinedirection) and in the width direction (transverse direction).

[0011] The polyester film includes films comprising aromatic polyesters(homopolymers) represented by polyethyelene terephthalate, polyethylene2,6-naphthalenedicarboxylate, and polybutylene terephthalate, or thefilms of these copolymers. Among the polymers, the polyethyleneterephthalate and the polyethylene 2,6-naphthalenedicarboxylate arepreferable from the viewpoint of uniform film-forming properties.

[0012] The polyester film may be a mono-layered film or a laminate filmcomprising two or more layers, and may be a balanced film whosemechanical properties are approximately equal in two axial directions ora reinforced film which is reinforced in one axial direction.

[0013] The polyester film may contain inner deposited particlesdeposited on the polymerization of the polyester, and inactive particlesadded before the formation of the film, such as inactive inorganicparticles represented by calcium carbonate particles, alumina particles,spherical silica particles, and titanium oxide particles, and organicparticles represented by cross-linked silicone resin particles,cross-linked polystyrene resin particles, cross-linked acrylic resinparticles, cross-linked polyester resin particles, cross-linkedstyrene-acrylic resin particles, polyimide particles, melamine resinparticles.

[0014] The average particle diameter of these inactive particles ispreferably not less than 0.0 μm and not more than 2.0 μm. The lowerlimit of the average particle diameter is further preferably 0.05 μm,furthermore preferably 0.1 μm, while the upper limit is furtherpreferably 1.0 μm, furthermore preferably 0.7 μm. The content of theinactive particles is preferably not less than not less than 0.001percent by weight and not more than 2.0 percent by weight. The lowerlimit of the content is further preferably 0.005 percent by weight,furthermore preferably 0.01 percent by weight, while the upper limit isfurther preferably 1.0 percent by weight, furthermore 0.5 percent byweight.

[0015] The polyester film roll in the present invention is the film rollwhich the polyester film is rolled on the core, and needs that thedifference R (m) between the maximum value and the minimum value is notmore than 2W×10⁻³ and not more than L×10⁻⁷, when the diameters of saidroll are measured in the width direction of the roll. Preferably, R (m)is preferably not more than 1.5W×10⁻³ and not more than (L/1.5)×10⁻⁷.Therein, W is the width (m) of the film roll, and L is the rolled length(m) of the film roll.

[0016] In the case of not satisfying the above-described equations, thepolyester film roll is not preferable, because the accumulated thicknessunevenness of the roll shape is enlarged, thereby easily generatingwrinkles on the roll in the thin portion of the film and easilyextending the thick portion to generate slack on the film, when the filmis unrolled from the roll. Even when the polyester film roll does nothave a local uneven portion in the profile of the roll shape but whenthe whole shape of the polyester film roll is obliquely inclined, thepolyester film roll is also not preferable, because one side (on thelarger diameter side of the roll) of the film is slackened on theunrolling of the film from the roll and because the rolling of the filmis shifted on the rolling of the film in the next process, althoughwrinkles are scarcely generated.

[0017] A method for producing the above-described polyester film roll isespecially not limited, but preferably includes a method comprisingmeasuring the thickness of the continuously produced and traveling filmin high accuracy or measuring the roll shape values (diameters) of therolled film roll in the width direction, and then feeding back themeasured values to adjust the temperature and gap of die lips so as tosatisfy the shape of the roll of the present invention, thus adjustingthe thickness of the film. The former high accuracy measurement methodis the most ideal method, because of enabling the control in highresponse, but the latter method can be combined with a conventionalthickness unevenness-adjusting method and also has advantages that theaccuracy shortage of said method is covered and that an increase in thecost is restrained. In the former method for measuring the thickness ofthe traveling film, a non-contact type hardness meter generally usedonline, such as a transmitted β-ray attenuation method thickness meter,a transmitted infrared light attenuation method thickness meter, or anoptical interferencial spectoscopy thickness meter, is used. In thelatter roll shape method, a stylus type thickness meter, a non-contactlaser type thickness meter, or the like, is also used.

[0018] The degree of rolling hardness of the polyester film roll in thepresent invention is preferably not less than 90 and not more than 100,further preferably not less than 95 and not more than 100. When thedegree of rolling hardness is less than 90, the polyester film rolltends to generate wrinkles with the passage of time, and is furtherliable to cause the slippage of the rolled film.

[0019] The width and length of the polyester film in the presentinvention are especially not limited, but are generally 0.300 to 1.500 mand 3,000 to 30,000 m, respectively, from the viewpoint of productivityin an industrial scale. The effects of the present invention especiallyremarkably appear on the roll of a film having a width of not less than0.400 m and a length of not less than 5,000 m. The thickness of the filmis preferably not less than 0.5 μm and not more than 20 μm, furtherpreferably not less than 3, m and not more than 10 μm. A film having athickness of less than 0.5 μm is inferior in a rolling property becausethe rigidity of the film is extremely low, while a film having athickness of more than 20 μm has high rigidity, therefore they scarcelyexpress the effects of the present invention.

[0020] The surface roughness Ra of the polyester film in the presentinvention is preferably not less than 0.1 nm and not more than 10 nm,further preferably not less than 0.3 nm and not more than 8 nm,especially preferably not less than 0.3 nm and not more than 5 nm. Whenthe Ra of the polyester film is less than 0.1 nm, the polyester film isnot preferable, because the polyester film has an inferior slippingproperty and gives only film rolls having extremely inferior rolledappearances. On the other hand, a coarse polyester film having a Ra ofmore than 10 nm hardly becomes the target of the present invention,because the polyester film scarcely generates wrinkles, even when theshape of the roll does not satisfy the conditions of the presentinvention.

[0021] The outer diameter of the roll-shaped core of the polyester filmroll in the present invention is especially not limited, but is usually0.100 to 0.400 m. When the outer diameters of the roll shape of the coreare measured in the width direction of the core, the difference (Rc)between the maximum value and the minimum value is preferably not morethan 300×10⁻⁶ m, further preferably 200×10⁻⁶ m. When the difference (Rc)exceeds 300×10⁻⁶ m, the core is not preferable, because wrinkles andslacks are generated in the film roll by the effect of the core, evenwhen the thickness unevenness of the polyester film is small. The rollshape of the core is desirably a crown shape in which the centralportion of the core in the width direction and both the end portions ofthe core are thick and thin, respectively. The crown shape facilitatesthe outward removal of air between the films and the inhibition ofwrinkle generation, when the polyester film is rolled. In the core ofthe crown shape, the difference between the diameter of the centralportion and the diameters of both the end portions is preferably in therange of 0 m to 300×10⁻⁶ m.

[0022] As a material for the above-described core, paper, a plastic orthe like may be used, but a fiber-reinforced plastic is preferably usedfrom the viewpoint of strength. The core produced from thefiber-reinforced plastic includes a core produced by winding around, forexample, carbon fibers or glass filaments in a cylindrical shape,impregnating the cylindrical product with a thermosetting resin such asan unsaturated polyester resin and then curing the impregnation product.

[0023] The flexural modulus of the above-described core in thecircumferential direction is preferably not less than 13 GPa, furtherpreferably not less than 14 GPa. When the core having the flexuralmodulus not satisfying the range is used, the core is often deformed bya tension and a contact pressure generated when the polyester film isrolled. A method for adjusting the strength of the core within the rangeis especially not limited, but the strength of, for example, a carbonfiber-reinforced plastic core can be adjusted by suitably selecting theamount of the carbon fibers, and a desired strength is further obtainedby adjusting the thickness of the core.

[0024] The surface roughness Ra of the above-described core ispreferably not more than 0.6 μm, further preferably not more than 0.3μm. When a core not satisfying the range is used, the surface roughnessof the core is transferred to the surface of a polyester film. Thereby,when the core is used for, for example, a film which is used for a highrecording density magnetic tape severely demanding the flatness of thefilm, the electromagnetic transducing properties of the magnetic tape issometimes remarkably deteriorated. A method for controlling the surfaceroughness of the core within the range is especially not limited, but adesired surface roughness is obtained, for example, by disposing a resinlayer on the surface of the core and then grinding the surface of theresin layer in good accuracy.

[0025] The degree of surface hardness of the core is preferably not lessthan 65 degree, further preferably not less than 70 degree. When a corenot satisfying the range is used, the core is often deformed by atension and a contact pressure generated on the rolling of the polyesterfilm, and the deformation is often transferred to the film to produce adefective flat surface. A method for adjusting the degree of surfacehardness of the core within the range is especially not limited, but thedegree of surface hardness of the core can be adjusted by using a hardresin such as an epoxy resin on the surface of the core and thensuitably selecting the thickness.

[0026] The polyester film roll in the present invention is especiallyeffective as a film roll for magnetic recording media which demand goodflatness. The polyester film roll is effective as a polyester film rollfor digital recording method magnetic recording media among the magneticrecording media. Furthermore, among them, the polyester film roll in thepresent invention is effective as a polyester film roll, for magneticrecording media of ferromagnetic metal thin film layers, whose magneticlayer-formed side film surfaces demand the ultimate flatness, and whosenon-magnetic side film surfaces also demand flatness from the viewpointof thermal deterioration on vacuum deposition, besides maintaining of arolling-up property.

[0027] The degree of rolling hardness of the polyester film roll in thepresent invention is preferably adjusted to not less than 90 and notmore than 100 to prevent the generation of wrinkles with the passage oftime and the slippage of the rolled film as described above. In order toobtain the roll having such the degree of hardness, the polyester filmis preferably rolled under conditions comprising a rolling tension of 5to 20 kg/m, a rolling contact pressure of 50 to 200 kg/m, a rollingspeed of 20 to 200 m/minute, further preferably 40 to 200 m/minute. Whenthe polyester film roll is used as a magnetic recording medium, acoating layer for facilitating the adhesion or slipping of the polyesterfilm is very often disposed on the magnetic layer-forming side surfaceof the polyester film. Therein, the polyester film is preferably rolledso that the magnetic layer-forming side surface of the film is arrangedon the inner side to prevent the coating layer from being shaven with acontact pressure roll of a slitter.

[0028] Subsequently, the second polyester film roll of the presentinvention will be explained.

[0029] On the second polyester film, it should be understood that thedescriptions on the first polyester roll may be applied as such tomatters not described below.

[0030] The polyester film roll in the present invention is a polyesterfilm roll in which a polyester film is rolled on a core, and which,among the lengths of lines which are obtained by measuring the diametersof said roll in the width direction of the roll, drawing a straight linebetween both the ends of the curved line of the obtained roll diameters,and then vertically drawing the lines from said curved line to saidstraight line, the maximum length (maximum convex portion) on the convexportion side from said straight line is not more than 500 μm, preferablynot more than 400 μm, especially preferably not more than 300 μm, andthe maximum length (maximum concave portion) on the concave portion sidefrom said straight line is not more than 300 μm, preferably not morethan 200 μm, especially preferably not more than 150 μm.

[0031] When the maximum convex portion exceeds 500 μm, the film at theplace is extended to cause problems such as the generation ofCaterpillar rut-like wrinkles (slacks), the deterioration of theflatness, the failure in the formation of an uniform coating film, thegeneration of wrinkles to make it impossible to uniformly calender thefilm, when the film is calendered, and the generation of magnetic tapeshaving smaller widths than a desired width, when slit into magnetictapes. When the maximum concave portion exceeds 300 μm, air isaccumulated at the portion in the width direction of the roll and causesproblems such as the formation of longitudinal wrinkles, when the air isremoved, the failure in the formation of an uniform coating film, andthe failure in a uniform calendering operation, when the film iscalendered.

[0032] The method for producing the above-described polyester film rollis especially not limited, but preferably includes methods comprisingmeasuring the thickness of a continuously formed traveling film in highaccuracy, or using a die having a narrowed lip heater distance so as toenable the fine control in the thickness of the film, or properlysetting an oscillation width on a slitting operation, or adjusting thethickness of the film by measuring the roll shape values (diameters) ofthe rolled film roll in the width direction of the roll, and then byfeeding back the measured values to adjust the temperature and gap ofthe die lips so as to satisfy the roll shape of the present invention.The former highly accurate measuring method is the most ideal method,because the thickness of the film can be controlled in high response.But, the latter method can be combined with conventional thicknessunevenness-adjusting methods, and has advantages that the shortage inthe accuracy of the method can be covered and that an increase in thecost can be restrained. A non-contact method hardness meter, generallyused online, such as a transmitted β-ray attenuation method thicknessmeter, a transmitted infrared light attenuation method thickness meter,or an optical interferencial spectoscopy thickness meter, is used formeasuring the thickness of the traveling film by the former method. Anda stylus type thickness meter, a non-contact laser type thickness meter,or the like, is used for the latter roll shape method.

[0033] The width and length of the polyester film in the presentinvention are especially not limited, but the width and the length aregenerally not less than 300 mm and not more than 1,500 mm, and not lessthan 3,000 m and not more than 30,000 m, respectively, from theviewpoint of productivity in an industrial scale. The effects of thepresent invention especially remarkably appear on the roll of a filmhaving a width of not less than 500 mm and a length of not less than4,000 m. Also, the effects especially remarkably appear on the roll of afilm having a thickness of not less than 2 μm and not more than 10 μm,further preferably of not less than 3 μm and not more than 8 μm,especially preferably of not less than 4 μm and not more than 7 μm. Afilm having a thickness of less than 2 μm is difficult to be used as thesupport of a magnetic recording medium, because the rigidity of the filmis extremely lowered, while a film having a thickness of more than 10 μmis difficult to become the target of the present invention, because thefilm has a high rigidity and gives a relatively good rolled appearance.

[0034] The polyester film in the present invention exhibits theremarkable effects, when at least one surface roughness Ra of thepolyester film is preferably not less than 0.1 nm and not more than 10nm, further preferably not less than 0.3 nm and not more than 8 nm,especially preferably not less than 1 nm and not more than 6 nm. Thepolyester film having a surface roughness Ra of less than 0.1 nm is notpreferable, because the polyester film has an inferior slipping propertyand gives only film rolls having extremely inferior rolled appearances.On the other hand, a coarse polyester film having a Ra of more than 10nm hardly becomes the target of the present invention, because thepolyester film scarcely generates wrinkles even when the shape of theroll does not satisfy the conditions of the present invention.

[0035] The outer diameter of the roll-shaped core of the polyester filmroll in the present invention is especially not limited, but is usually80 to 200 mm. And, it is preferable to use the core, wherein, among thelengths of lines which are obtained by measuring the diameters of thefilm-rolling portion of the core in the width direction of the core,drawing a straight line between both the ends of the curved line of theobtained core diameters, and then vertically drawing the lines from saidcurved line to said straight line, the maximum length (maximum convexportion) on the convex portion side from said straight line is not morethan 400 μm, preferably not more than 200 μm, especially preferably notmore than 100 μm, and the maximum length (maximum concave portion) onthe concave portion side from said straight line is not more than 200μm, preferably not more than 100 μm, especially not more than 50 μm.Even when the thickness unevenness of the polyester film is little, thecore in which the maximum convex portion exceeds 400 μm or in which themaximum concave portion exceeds 200 μm is not preferable, becauselongitudinal wrinkles and slacks are generated on the film roll by theeffect of the core.

[0036] As described above, it should be understood that the descriptionson the first polyester film roll are applied as such to matters notdescribed herein on the second polyester film roll of the presentinvention.

[0037] (The Uses of the Polyester Film Roll)

[0038] In the present invention, as understood from the above-describedexplanations, the polyester films obtained from the first polyester filmroll and the second polyester film roll can advantageously be used assupports (base films) for magnetic recording media, capacitors,packages, printing materials, and so on, especially as supports for highdensity magnetic recording media (video tapes, audio tapes, computertapes, and so on).

EXAMPLES

[0039] Hereinafter, the present invention will further be explained withexamples, but the present invention is not limited to thebelow-described examples, so long as not exceeding the essential pointsof the present invention. And, the characteristic values were measuredby the following methods.

[0040] Polyethylene terephthalate of raw material is melted and extrudedin a filmy shape by the use of an extruder, cooled, oriented in themachine direction at a draw ratio of 3 to 6, and then oriented in thetransverse direction at a draw ratio of 3 to 6. Between themachine-direction orienting process and the transversely orientingprocess a coating liquid may be coated on the side of the film todispose a coating layer. The film may further be reoriented in themachine direction and in the transverse direction. The film is thenthermally set to form the polyester film having a thickness in a rangeof 0.5 to 20 μm, preferably in a range of 2 to 10 μm, which is rolled,for example, as a jumbo roll. Therein, as described above, the thicknessof the traveling film is accurately measured by an online measuringmethod, or the roll shape values of the rolled film roll in the widthdirection are measured. The measured values are fed back for theadjustment of the temperature and gap of die lips so as to satisfy theroll shape of the present invention, thus adjusting the thickness of thefilm. The film is slit into films having prescribed widths and lengthsby the use of a slitter. When the film is slit, the jumbo roll may beoscillated to disperse the thickness unevenness in the width direction.By the oscillation, roll shape defects due to small thickness unevennesscan be reduced. When the film is slit, the obtained films are adhered tocores with a paste, adhesive tapes, or a liquid such as water or analcohol. The obtained films are rolled in a prescribed length, while adesired rolling tension and a desired rolling contact pressure areapplied to the films with the slitter.

[0041] (1). The Surface Roughness Ra of the Film

[0042] According to JISB 0601, the center line average roughness of thefilm is determined with a stylus type surface roughness meter (surfcoderSE30FAT) manufactured by (Ltd.) Kosaka Kenkyusho under conditionscomprising a stylus tip radius of 2 μm, a measuring pressure of 30 mg, acutoff of 0.08 m and a measuring length of 1.25 mm. The measurements arecarried out four times, and the average value is used as the surfaceroughness Ra of the film.

[0043] (2). The Shapes of the Polyester Film Roll and the Core in theWidth Direction

[0044] (2-1). The Case of the First Polyester Film Roll

[0045] The roll shape of the film roll is measured with a bulk shapemeasurer manufactured by Kitano Kikaku (Ltd.) in the width direction,and a difference R(m) between the maximum value and the minimum value ofthe measured diameters is determined. Each diameter is determined bymeasuring diameters at three positions at a distance of 120 degree inthe circumferential direction and then the measured values are averaged.The measured data in the ranges of both the ends of the film roll to0.010 m positions are deleted to remove the effects of the high edges ofthe film end surfaces.

[0046] (2-2). The Case of the Second Polyester Film Roll

[0047] The roll shape of the film roll is measured with a bulk shapemeasurer manufactured by Kitano Kikaku (Ltd.) in the width direction,and a curved line showing the change of the diameters is determined.Each diameter is determined by measuring diameters at three positions ata distance of 120 degree in the circumferential direction and then themeasured values are averaged. Both the ends of the curved line are boundto each other to form a straight line. Lines are vertically drawn fromconvex portions to the obtained straight lines, and the maximum convexportion is determined. Lines are also vertically drawn from concaveportions to the straight line, and the maximum concave portion isdetermined. The measured data in the ranges of both the ends of the filmroll to 0.01 m positions are deleted to remove the effects of the highedges of the film end surfaces.

[0048] The film-rolling portion of the core on which the film is rolledis also measured as described above, and the maximum convex portion andthe maximum concave portion are determined.

[0049] (3). The Degree of Surface Hardness of the Polyester Film Roll

[0050] A hardness tester, type C, manufactured by Kobunshi Keiki (Ltd.)is pressed on the polyester film roll to measure the degree of surfacehardness. Measuring points are totally 15 measuring points which consistof three measuring points at a distance of 120 degree in thecircumferential direction at each of five points in the width directionof the polyester film roll (wherein the width obtained by removing boththe 0.010 m long end widths from the overall width of the roll isdivided into five equal portions, and the measurements are carried outat the three measuring positions in the center of each of the equalportions).

[0051] (4). The Flexural Modulus of the Core in the CircumferentialDirection

[0052] The flexural modulus is determined by measuring the deflection ofa ring-like test piece (width: 50 mm) with a universal tester, when aload is applied to the test piece in the circumferential direction, andthen substituting the measured value into the following equation.

Eγ=0.149Pr ³/(δI)*10⁻³,

[0053] wherein, cross-sectional secondary moment I=50t³/12

[0054] Eγ; elastic modulus (GPa) in the circumferential direction

[0055] P; load (N)

[0056] r; central diameter (mm)

[0057] t: deflection (mm)

[0058] t; core thickness (mm).

[0059] (5). The Degree of Surface Roughness Rac of the Core

[0060] According to JIS B0601, the degree of surface roughness Rac ofthe core is determined by measuring a degree of central line averageroughness at the center of the core in the width direction and at twopositions apart from both the ends at distances of 0.050 m with cutoffsof 0.25 mm, respectively, by the use of Surfcom 111 A, a surfaceroughness meter of Tokyo Seimitsu (Ltd.) and then averaging the measuredvalues.

[0061] (6). The Degree of Surface Hardness of the Core

[0062] According to the JIS K7215, the degree of surface hardness of thecore is determined by pressing a hardness tester, type D manufactured byKobunshi Keiki (Ltd.) on the center of the core in the width directionand on places apart from both the ends of the core at distances of 0.050m, respectively, to measure the degrees of surface hardness at the threepositions and then averaging the measured values.

[0063] (7). Young's Modulus

[0064] The Young's modulus is determined by cutting off a test piecehaving a width of 10 mm and a length of 150 mm from the film, pullingthe test piece at a distance of 100 mm between the chucks of an instrontype universal tensile tester at a pulling rate of 10 mm/minute and at achart rate of 500 mm/minute and then calculating the Young's modulusfrom the tangential line at the standing-up portion of the obtainedload-elongation curve.

Comparative Example 1

[0065] The pellets of polyethylene 2,6-naphthalenedicarboxylatesubstantially not containing inactive particles were dried at 170° C.for 6 hours, fed into an extruder and then melted at 305° C. The meltedpolymer was filtered by a known method, extruded from the extruder intoa sheet-like product, and then quenched and solidified on a casting drumto produce the non-oriented film. Subsequently, the non-oriented filmwas preliminarily heated at 120° C., machine-direction oriented betweena low speed roll and a high speed roll at an orientation ratio of 3.7under a 900° C. IR heater disposed at a height of 15 mm above the film,and then coated with aqueous solutions having the followingcompositions, respectively.

[0066] The Side of the Surface A

[0067] a copolyester (terephthalic acid/isophthalic acid/5-sodiumsulfoisophthalic acid//ethyleneglycol/bisphenol A·two propyleneoxideadduct=97/1/2//60/40): 80 parts.

[0068] acrylic particles (average particle diameter: 30 nm): 5 parts.

[0069] SS-70 produced by Sanyo Kasei: 15 parts.

[0070] thickness (after dried): 5 nm.

[0071] The Side of the Surface B

[0072] a copolyester (terephthalic acid/isophthalic acid/5-sodiumsulfoisophthalic acid//ethyleneglycol/bisphenol A·two propyleneoxideadduct=9711/2//60/40): 60 parts.

[0073] acrylic particles (average particle diameter: 40 nm): 10 parts.

[0074] hydroxyethylmethylcellulose: 20 parts.

[0075] Nonion NS-208.5 produced by Nippon Yushi: 10 parts.

[0076] thickness (after dried): 20 nm.

[0077] Subsequently, the film was fed into a stenter, oriented at aorientation ratio of 4.9 in the transverse direction at 150° C., furtheroriented at a ratio of 1.14 in the transverse direction at 200° C. andsimultaneously thermally treated to obtain the biaxially oriented filmhaving a thickness of 4.7 μm, which is rolled as a jumbo roll. Theobtained biaxially oriented film has a Ra of 0.7 nm on the surface A and3.3 nm on the surface B. The thickness of the biaxially oriented filmwas measured by the online scanning of a transmitted β-ray attenuationmethod thickness meter in the width direction, and the measurementresults were fed back to the temperatures of the die lips to control thethickness of the film. The jumbo roll was rerolled on a fiber-reinforcedplastic (FWP) core into a film roll having a width of 0.500 m, a lengthof 9,000 m and a rolling hardness of 99 degree under conditionscomprising a rolling tension of 10 kg/m, a rolling contact pressure of140 kg/m, a rolling rate of 100 m/minute, an oscillation width of 0.100m, and an oscillation rate of 0.010 m/minute. The fiber-reinforcedplastic (FWP) core had a length of 0.550 m, a crown-like shape, adifference of 120×10⁻⁶ m between the maximum diameter and the minimumdiameter in the width direction, a flexural modulus of 15.7 GPa in thecircumferential direction, a degree of surface roughness of 0.2 μm and adegree of surface hardness of 85 degree. The shape of the film roll inthe width direction was measured with a bulk shape measurer manufacturedby Kitano Kikaku (Ltd.). But, the shape of the roll did not satisfy thespecifications of the present invention, and wrinkles were generated onthe roll.

Example 1

[0078] A jumbo roll of a biaxially oriented film having a thickness of4.7 μm was produced and then slit by the same method as in thecomparative example 1 except that the roll shape of the obtained filmroll was measured and then fed back for the adjustment of thetemperatures of die lips and for the adjustment of the gap between thelips to reduce the thickness unevenness of the film. The shape of theobtained film roll in the width direction was measured. It wasconsequently found that the film roll had the roll shape satisfying theconditions of the present invention, and wrinkles were not recognized onthe roll not only just after slit but also after the passage of 24hours.

Comparative Example 2

[0079] On the production of the film in the comparative example 1, thefilm of the jumbo roll was rerolled on a fiber-reinforced plastic (FWP)core to form a film roll having a width of 0.620 m, a length of 7,000 mand a degree of rolling hardness of 98 degree under conditionscomprising a rolling tension of 10 kg/m, a rolling contact pressure of100 kg/m, a rolling rate of 100 m/minute, an oscillation width of 0.100m, and an oscillation rate of 0.010 m/minute. The fiber-reinforcedplastic (FWP) core had a length of 0.67 m, a crown-like shape, adifference of 150×10⁻⁶ m between the maximum diameter and the minimumdiameter in the width direction, a flexural strength of 15.7 GPa in thecircumferential direction, a degree of surface roughness of 0.2 μm and adegree of surface hardness of 85 degree. The shape of the film roll inthe width direction was measured with a bulk shape measurer manufacturedby Kitano Kikaku (Ltd.). But, the shape of the roll did not satisfy thespecifications of the present invention, and wrinkles were generated onthe roll.

Example 2

[0080] A jumbo roll of a biaxially oriented film having a thickness of4.7 μm was obtained and then slit by the same method as in thecomparative example 2 except that the roll shape of the obtained filmroll was measured and then fed back for the adjustment of thetemperature of the die lips and for the adjustment of the gap betweenthe die lips to flatten the unevenness of the roll shape andsimultaneously reduce the thickness unevenness of the film. The shape ofthe obtained film roll in the width direction was measured. It wasconsequently found that the film roll had the roll shape satisfying theconditions of the present invention, and wrinkles were not recognized onthe roll not only just after slit but also after the passage of 24hours.

Comparative Example 3

[0081] On the production of the polyester film in the comparativeexample 1, the polyethylene 2,6-naphthalenedicarboxylate was changedinto polyethylene terephthalate, and the polyethylene terephthalate wasprocessed similarly except the following conditions to obtain a 6.4 μmthick biaxially oriented film. The conditions comprise a pellet dryingtime of 3 hours, a melting extrusion temperature of 295° C., amachine-direction orienting pre-heating temperature of 80° C., alongitudinal orientation ratio of 3.0, coating only the surface A withthe same coating liquid as that coated on the surface A in thecomparative example 1, transversely orienting the film at a orientationratio of 3.3 at 105° C., further transversely orienting the film at aorientation ratio of 1.6 at 210° C., and simultaneously thermallytreating the film. The Ra of the obtained biaxially oriented film was0.7 nm on the surface A and 3.0 nm on the surface B. A film roll wasproduced under the same slitting condition as in the comparativeexample 1. But, the shape of the roll did not satisfy the conditions ofthe present invention, and wrinkles are generated on the roll.

Example 3

[0082] A jumbo roll of a 6.4 μm-thick biaxially oriented film wasobtained and then slit by the same method as in the comparative example3 except operations comprising measuring the shape of the obtained filmroll, feeding back the measurement results to the temperature of the dielips and to the gap between the die lips to flatten the unevenness ofthe roll shape, and simultaneously controlling the thickness of thefilm. The shape of the obtained film roll in the width direction wasmeasured. It was consequently found that the film roll had the rollshape satisfying the conditions of the present invention, and wrinkleswere not recognized on the roll not only just after slit but also afterthe passage of 24 hours.

Comparative Example 4

[0083] On the production of the polyester film in the comparativeexample 1, a 4.7 μm-thick biaxially oriented polyester film was obtainedby the same method as in the comparative example 1 except operationscomprising changing the extrusion of polyethylene2,6-naphthalenedicarboxylate substantially not containing inactiveparticles to the coextrusion of a raw material A comprising polyethylene2,6-naphthalenedicarboxylate substantially not containing inactiveparticles and a raw material B comprising polyethylene2,6-naphthalenedicarboxylate substantially not containing inactiveparticles and containing 0.3 wt. % of silica particles having an averageparticle diameter of 300 nm in a thickness ratio of 3:2, and changingcoating the surfaces A and B with the coating liquids to coating onlythe surface A with the same coating liquid as that coated on the surfaceA in the comparative example 1. The Ra of the obtained film was 1.3 nmon the surface A and 5.8 nm on the surface B. A film roll was producedunder the same slitting condition as in the comparative example 1. But,the shape of the film roll did not satisfy the conditions of the presentinvention. The rolled appearance of the film roll was good just afterslit, but wrinkles were generated on the roll after the passage of 24hours.

Example 4

[0084] A jumbo roll of a 4.7 μm-thick biaxially oriented film wasobtained and then slit by the same method as in the comparative example4 except operations comprising measuring the roll shape of the obtainedfilm roll, feeding back the measurement results to the temperatures ofdie lips and to the gap between the die lips to flatten the unevennessof the roll shape, and simultaneously controlling the thickness of thefilm. The shape of the obtained film roll in the width direction wasmeasured. It was consequently found that the film roll had the rollshape satisfying the conditions of the present invention, and wrinkleswere not recognized on the roll not only just after slit but also afterthe passage of 24 hours. TABLE 1 The Rolled Appearance of the Roll RollAt the W L 2W × 10⁻³ L × 10⁻⁷ R Just after Passage of 24 [m] [m] [10⁻⁶m][10⁻⁶m] [10⁻⁶m] Slit hours after Slit Example 1 0.500 9,000 1,000 900300 Very good Very good Example 2 0.620 7,000 1,240 700 220 Very goodVery good Example 3 0.500 9,000 1,000 900 250 Very good Very goodExample 4 0.500 9,000 1,000 900 350 Very good Very good Comparative0.500 9,000 1,000 900 1,200 Bad Bad Example 1 Comparative 0.620 7,0001,240 700 810 Bad Bad Example 2 Comparative 0.500 7,000 1,000 700 950Bad Bad Example 3 Comparative 0.500 9,000 1,000 900 1,030 Good BadExample 4

[0085] As apparent from Table 1, the polyester film roll of the presentinvention did not have wrinkles generated thereon, and had a good rolledappearance.

Comparative Example 5

[0086] The pellets of polyethylene 2,6-naphthalenedicarboxylatecontaining 0.02 percent by weight of calcium carbonate having an averageparticle diameter of 0.6 μm and 0.3 percent by weight of sphericalsilica particles having an average particle diameter of 0.1 μm weredried at 170° C. for 6 hours, fed into an extruder and then melted at305° C. The melted polymer was filtered by a known method, extruded froma die having a lip gap of 60 mm, and then quenched and solidified on acasting drum to obtain the unoriented film. The unoriented film waspreliminarily heated at 120° C., further heated with a 900° C. IR(infrared light) heater disposed at a 15 mm-high place, oriented at aratio of 4.7 in the machine direction between a low speed roll and ahigh speed roll, fed into a stenter, oriented at a ratio of 5.0 in thetransverse direction at 150° C., and then thermally treated at 200° C.to obtain the 6.0 μm-thick biaxially oriented film, which was rolled asa jumbo roll. The obtained biaxially oriented film had a Ra of 8 nm, aYoung's modulus of 6.9 GPa in the machine direction and a Young'smodulus of 7.2 GPa in the transverse direction. The thickness of thebiaxially oriented film was measured by the online scanning of atransmitted β-ray attenuation method thickness meter in the widthdirection, and the measurement results were fed back to the temperaturesof the die lips to control the thickness of the film. The film of thejumbo roll was rerolled on a fiber-reinforced plastic (FWP) core througha slitter under conditions comprising a rolling tension of 10 kg/m, arolling contact pressure of 140 kg/m, a rolling rate of 100 m/minute, anoscillation width of 100 mm, and an oscillation rate of 0.010 m/minuteto obtain the film roll having a width of 1.0 m, a length of 5,000 m anda degree of rolling hardness of 99 degree. The fiber-reinforced plastic(FWP) core had a length of 1.2 m, the maximum convex portion of 100 μmand the maximum concave portion of 100 μm in the width direction, aflexural strength of 15.7 GPa in the circumferential direction, a degreeof surface roughness of 0.2 μm and a degree of surface hardness of 85degree. The shape of the film roll in the width direction was measuredwith a bulk shape measurer manufactured by Kitano Kikaku (Ltd.), and astraight line was drawn between both the ends of the curved line of themeasured diameters. Lines were vertically drawn from convex portions tothe straight line, and among the lengths of the lines, the length of themaximum convex portion was 700 μm. Lines were also vertically drawn fromconcave portions to the straight line, and among the lengths of thelines, the length of the maximum concave portion was 400 μm. After thepassage of 24 hours, the film was pulled out from the film roll, and theflatness of the film was examined. Consequently, the generation ofCaterpillar rut-like wrinkles (slackened wrinkles) was recognized at themaximum convex portion, and the generation of longitudinal wrinkles wasalso found out at the maximum concave portion. Thus, the film was bad inthe flatness, and had the problem in practical use.

Example 5

[0087] A jumbo roll of a biaxially oriented film was obtained and thenslit to give a film roll by the same method as in the comparativeexample 5 except the employment of a die having a lip gap of 30 mm (thelip gap of the die was a half of that in the comparative example 5). Theshape of the obtained film roll in the width direction was measured witha bulk shape measurer manufactured by Kitano Kikaku (Ltd.) by a similarmethod as in the comparative example 5. Among the lengths of lines whichwere obtained by measuring the shape of the film roll in the widthdirection, drawing a straight line between both the ends of the obtainedcurved line, and then vertically drawing the lines from the convexportions to the straight line, the length of the maximum convex portionwas 450 μm, and among the lengths of lines which were similarly obtainedby vertically drawing the lines from the concave portions to thestraight line, the length of the maximum concave portion was 250 μm.After the passage of 24 hours, the film was pulled out from the filmroll, and the flatness of the film was examined. Consequently, thegeneration of Caterpillar rut-like wrinkles (slackened wrinkles) wasslightly recognized at the maximum convex portion, and the generation oflongitudinal wrinkles was also slightly found out at the maximum concaveportion. However, the Caterpillar rut-like wrinkles and the longitudinalwrinkles disappeared, when the film was lightly pulled. Thereby, theCaterpillar rut-like wrinkles and the longitudinal wrinkles did notcause a trouble in practical use.

Example 6

[0088] A jumbo roll of a biaxially oriented film was obtained and thenslit to give a film roll by the same method as in the comparativeexample 5 except that the oscillation width was changed to 150 mm (lipgap×transverse orientation ratio). The shape of the obtained film rollin the width direction was measured with a bulk shape measurermanufactured by Kitano Kikaku (Ltd.) by the same method as in thecomparative example 5. Among the lengths of lines which were obtained bymeasuring the shape of the film roll in the width direction, drawing astraight line between both the ends of the obtained curved line, andthen vertically drawing the lines from the convex portions to thestraight line, the length of the maximum convex portion was 250 μm, andamong the lengths of lines which were similarly obtained by verticallydrawing the lines from the concave portions to the straight line, thelength of the maximum concave portion was 150 μm. After the passage of24 hours, the film was pulled out from the film roll, and the flatnessof the film was examined. Consequently, the generation of Caterpillarrut-like wrinkles (slackened wrinkles) was not recognized at the maximumconvex portion, and the generation of longitudinal wrinkles was also notfound out at the maximum concave portion. Thereby, the flatness of thefilm was very good.

Example 7

[0089] A jumbo roll of a biaxially oriented film was obtained by thesame method as in the example 6. The shape of the obtained film roll inthe width direction was measured with a bulk shape measurer manufacturedby Kitano Kikaku (Ltd.), and die lip heaters corresponding to thepositions of the convex portions and concave portions of the obtainedcurved line of the roll shape were adjusted together with the onlineautomatic control of a transmitted β-ray attenuation method thicknessmeter. The jumbo roll obtained thus was slit to give a film roll by thesame method as in the example 6. The shape of the obtained film roll inthe width direction was measured with the bulk shape measurermanufactured by Kitano Kikaku (Ltd.) by the same method as in theexample 6. Among the lengths of lines which were obtained by drawing astraight line between both the ends of the obtained curved line and thenvertically drawing the lines from the convex portions to the straightline, the length of the maximum convex portion was 200 μm, and among thelengths of lines which were similarly obtained by vertically drawing thelines from the concave portions to the straight line, the length of themaximum concave portion was 100 μm. After the passage of 24 hours, thefilm was pulled out from the film roll, and the flatness of the film wasexamined. Consequently, the generation of Caterpillar rut-like wrinkles(slackened wrinkles) was not recognized at the maximum convex portion,and the generation of longitudinal wrinkles was also not found out atthe maximum maximum concave portion. Thereby, the flatness of the filmwas very good.

Example 8

[0090] The pellets of polyethylene terephthalate containing 0.25 percentby weight of spherical silica particles having an average particlediameter of 0.1 μm and used for a layer A, and the pellets ofpolyethylene terephthalate containing 0.05 percent by weight ofcross-linked silicone resin particles having an average particlediameter of 0.6 μm and 0.4 percent by weight of alumina particles havingan average particle (secondary particle) diameter of 0.1 μm and used fora layer B were dried at 170° C. for 3 hours, fed into two extruderhoppers, respectively, melted at 300° C., and then extruded from amulti-manifold type coextruder die having a lip gap of 30 mm to obtainthe sheet-like laminate where the layer A is laminated to one side ofthe layer B in a ratio of 7:3. The extruded sheet-like laminate wasquenched and solidified on a casting drum to obtain the non-orientedfilm. The non-oriented film was preliminarily heated at 75° C., furtherheated with a 830° C. IR (infrared light) heater from a 14 mm-high placeand simultaneously oriented at a ratio of 2.3 in the machine directionbetween a low speed roll and a high speed roll, quenched, fed into astenter, oriented at a ratio of 3.6 in the transverse direction at 110°C., preliminarily heated at 110° C., oriented at a ratio of 2.5 betweena low speed roll and a high speed roll, further fed into a stenter, andthen thermally set at 210° C. for 10 seconds to obtain the 6.0 μm-thickbiaxially oriented film, which was rolled as a jumbo roll. The biaxiallyoriented film had a surface roughness Ra of 4 nm on the surface A, asurface roughness Ra of 8 nm on the surface B, a Young's modulus of 7.8GPa in the machine direction, and a Young's modulus of 4.7 GPa in thetransverse direction. The shape of the obtained jumbo roll in the widthdirection was measured with the bulk shape measurer manufactured byKitano Kikaku (Ltd.), and die lip heaters corresponding to the positionsof the convex portions and concave portions of the obtained curved lineof the roll shape were adjusted together with the online automaticcontrol of a transmitted β-ray attenuation method thickness meter. Thejumbo roll obtained thus was slit by the same method as in the example 7except that the oscillation width was changed to 110 mm, therebyobtaining a film roll. The shape of the obtained film roll in the widthdirection was measured with the bulk shape measurer manufactured byKitano Kikaku (Ltd.) by the same method as in the example 7. Among thelengths of lines which were obtained by drawing a straight line betweenboth the ends of the obtained curved line and then vertically drawingthe lines from the convex portions to the straight line, the length ofthe maximum convex portion was 150 μm, and among the lengths of lineswhich were similarly obtained by vertically drawing the lines from theconcave portions to the straight line, the length of the maximum concaveportion was 100 μm. After the passage of 24 hours, the film was pulledout from the film roll, and the flatness of the film was examined.Consequently, the generation of Caterpillar rut-like wrinkles (slackenedwrinkles) was not recognized at the maximum convex portion, and thegeneration of longitudinal wrinkles was also not found out at themaximum concave portion. Thereby, the flatness of the film was verygood.

Comparative Example 6

[0091] A jumbo roll of a biaxially oriented film was obtained, and thenslit to give a film roll by the same method as in the comparativeexample 5 except that the oscillation ratio was changed to 150 mm. Theshape of the obtained film roll in the width direction was measured witha bulk shape measurer manufactured by Kitano Kikaku (Ltd.) by the samemethod as in the example 1. Among the lengths of lines which wereobtained by drawing a straight line between both the ends of theobtained curved line, and then vertically drawing the lines from theconvex portions to the straight line, the length of the maximum convexportion was 550 μm, and among the lengths of lines which were alsosimilarly obtained by vertically drawing the lines from the concaveportions to the straight line, the length of the maximum concave portionwas 250 μm. After the passage of 24 hours, the film was pulled out fromthe film roll, and the flatness of the film was examined. Consequently,the generation of longitudinal wrinkles was slightly found out at themaximum concave portion. When the film was lightly pulled, the finelongitudinal wrinkles disappeared, and did not cause a trouble. However,the generation of Caterpillar rut-like wrinkles (slackened wrinkles)were recognized at the maximum convex portion to deteriorate theflatness of the film, and caused troubles in practical use.

Comparative Example 7

[0092] A jumbo roll of a biaxially oriented film was obtained by thesame method as in the comparative example 5. The shape of the obtainedjumbo roll in the width direction was measured with a bulk shapemeasurer manufactured by Kitano Kikaku (Ltd.), and die lip heaterscorresponding to the positions of the convex portions and concaveportions of the obtained curved line of the roll shape were adjustedtogether with the online automatic control of a transmitted β-rayattenuation method thickness meter. The jumbo roll obtained thus wasslit to give a film roll by the same method as in the comparativeexample 5. The shape of the obtained film roll in the width directionwas measured with the bulk shape measurer manufactured by Kitano Kikaku(Ltd.) by the same method as in the comparative example 5. Among thelengths of lines which were obtained by drawing a straight line betweenboth the ends of the obtained curved line and then vertically drawingthe lines from the convex portions to the straight line, the length ofthe maximum convex portion was 300 μm, and among the lengths of lineswhich were similarly obtained by vertically drawing the lines from theconcave portions to the straight line, the length of the maximum concaveportion was 350 μm. After the passage of 24 hours, the film was pulledout from the film roll, and the flatness of the film was examined.Consequently, the generation of Caterpillar rut-like wrinkles (slackenedwrinkles) were not recognized at the maximum convex portion, but thegeneration of longitudinal wrinkles were found out at the maximumconcave portion to deteriorate the flatness of the film was bad, andcaused troubles in practical use.

[0093] These results are shown in the table 2. As apparent from thetable 2, the polyester film roll of the present invention was free fromthe generation of wrinkles, had a good rolled appearance, and did notcause a trouble in practical use. TABLE 2 Unit E. 5 E. 6 E. 7 E. 8 C.E.5 C.E. 6 C.E. 7 Polymer PEN PEN PEN PET PEN PEN PEN Layer Single SingleSingle Two Single Single Single Constitution Layer Layer Layer LayersLayer Layer Layer Surface Roughness Layer A [nm] 7 7 7 4 7 7 7 Layer B[nm] 7 7 7 9 7 7 7 Total Ratio # 1 [Ratio] 4.7 4.7 4.7 5.75 4.7 4.7 4.7# 2 [Ratio] 5.0 5.0 5.0 3.6 5.0 5.0 5.0 # 3 [nm] 30 30 30 30 60 60 60 #4 [nm] 100 150 150 108 100 150 100 Roll Size Film [mm] 1,000 1,000 1,0001,000 1,000 1,000 1,000 Width Film [m] 5,000 5,000 5,000 5,000 5,0005,000 5,000 Length Roll Shape # 5 [μm] 450 250 200 150 700 550 300 # 6[μm] 250 150 100 100 400 250 350 Rolled Appearance of the Film Roll #7Good Very Very Very Bad Bad Good Good Good Good #8 Good Very Very VeryBad Good Bad Good Good Good

[0094] According to the present invention, a polyester film roll, whichdoes not generate wrinkles and slacks with the passage of time, givesnarrow slit film-products having accurate widths, and has a good rolledappearance even with flat surfaces, can be provided, without theproblems that the characteristics of a film must be changed as acountermeasure for a good rolled shape of a film roll, and that thecharacteristics of a film is also changed to improve the conventionaltechnical problems, such as, wrinkles and slacks are generated with thepassage of time, even if they are not found during rolling of the film;the width of the slit film for a magnetic tape is partially narrowedafter being slit from a wide film; and the development of thetechnologies for rolling a flat thin film is extremely difficult, sothat they are not applied for commercial production. Thereby, theindustrial value of the present invention is high.

1. A polyester film roll in which a polyester film is rolled on a core,characterized in that the difference R (m) between the maximum value andthe minimum value is not more than 2W×10⁻³ and not more than L×10⁻⁷,when the diameters of said roll are measured in the width direction ofthe roll, wherein, W is the width (m) of the film roll, and L is therolled length (m) of the film roll.
 2. The polyester film roll describedin claim 1, wherein the surface roughness Ra of the polyester film isnot less than 0.1 nm and not more than 10 nm.
 3. The polyester film rolldescribed in claim 1 or 2, wherein the thickness of the polyester filmis not less than 0.5 μm and not more than 20 μm.
 4. The polyester filmroll described in either one of claims 1 to 3, wherein the degree ofrolling hardness of the film roll is not less than 90 and not more than100.
 5. The polyester film roll described in either one of claims 1 to4, wherein the polyester film is a film comprising polyethyleneterephthalate or polyethylene 2,6-naphthalenedicarboxylate.
 6. Thepolyester film roll described in either one of claims 1 to 5, whereinthe difference (Rc) between the maximum value and the minimum value isnot more than 300×10⁻⁶ m, when the roll diameters of the core aremeasured in the width direction of the core.
 7. The polyester film rolldescribed in claim 1 or 6, wherein the roll shape of the core is a crownshape whose central portion is thick and whose both end portions arethin.
 8. The polyester film roll described in claim 1, 6 or 7, whereinthe core is a fiber-reinforced plastic core.
 9. The polyester film rolldescribed in either one of claims 1, 6 to 8, wherein the flexuralmodulus of the core in the circumferential direction is not less than 13Gpa.
 10. The polyester film roll described in either one of claims 1, 6to 9, wherein the degree of surface roughness Rac of the core is notmore than 0.6 μm.
 11. The polyester film roll described in either one ofclaims 1, 6 to 10, wherein the degree of surface hardness of the core isnot less than 65 degree.
 12. The polyester film roll described in eitherone of claims 1, to 11, wherein the polyester film is a film used forthe support of a magnetic recording medium.
 13. The polyester film rolldescribed in claims 12, wherein the magnetic recording medium is adigital recording method magnetic recording medium.
 14. The polyesterfilm roll described in claim 12 or 13, wherein the magnetic recordingmedium is a magnetic recording medium whose magnetic layer is aferromagnetic metal thin film layer.
 15. The polyester film rolldescribed in either one of claims 12 to 14, wherein the polyester filmhas a coating layer on the side on which the magnetic surface isdisposed and the surface with the coating layer is rolled in the innerside.
 16. A polyester film roll in which a polyester film is rolled on acore, characterized in that, among the lengths of lines which areobtained by measuring the diameters of said roll in the width directionof the roll, drawing a straight line between both the ends of the curvedline of the obtained roll diameters, and then vertically drawing thelines from said curved line to said straight line, the maximum length(maximum convex portion) on the convex portion side from said straightline is not more than 500 μm, and the maximum length (maximum concaveportion) on the concave portion side from said straight line is not morethan 300 μm.
 17. The polyester film roll described in claim 16, whereinthe roughness Ra of at least one of the surfaces of the polyester filmis 1 to 10 nm.
 18. The polyester film roll described in claim 16,wherein the thickness of the polyester film is 2 to 10 μm.
 19. Thepolyester film roll described in claim 16, wherein the degree of rollinghardness of the film roll is 90 to
 100. 20. The polyester film rolldescribed in claim 16, wherein the width of the film roll is not lessthan 300 mm, and the rolled length of the film roll is not less than4,000 m.
 21. The polyester film roll described in claim 16, wherein thepolyester film is a film comprising polyethylene terephthalate orpolyethylene 2,6-naphthalenedicarboxylate.
 22. The polyester film rolldescribed in claim 16, wherein the polyester film roll is supplied for amagnetic recording medium.
 23. The polyester film roll described inclaim 22, wherein the polyester film roll is supplied for a magneticrecording medium whose magnetic layer is a coating type.
 24. Thepolyester film roll described in claim 16, wherein, among the lengths oflines which are obtained by measuring the diameters of the film-rollingportion of the core in the width direction of the core, drawing astraight line between both the ends of the curved line of the obtainedcore diameters, and then vertically drawing the lines from said curvedline to said straight line, the maximum length (maximum convex portion)on the convex portion side from said straight line is not more than 400μm, and the maximum length (maximum concave portion) on the concaveportion side from said straight line is not more than 200 μm.